LIFE HISTORY PHASES AND THE BIOMECHANICAL PROPERTIES OF THE RED ALGA CHONDRUS CRISPUS (RHODOPHYTA)

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Abstract
Chondrus crispus Stackhouse alternates between two isomorphic life history phases that differ in cell‐wall phycocolloid composition. It has been long hypothesized that the gametophyte, with strong‐gelling kappa‐type carrageenans, is mechanically superior to the tetrasporophyte, with nongelling lambda‐type carrageenans, which could contribute to the observed gametophytic dominance in many wave‐swept environments. Standard mechanical tests were performed on distal tissues of C. crispus sampled from a range of environments in Narragansett Bay, Rhode Island, using a tensometer equipped with a video extensometer. Life history phase was by far the most important determinant of mechanical properties, whereas environmental factors had only modest influence (vertical distribution) or no effect (exposure); gametophytic distal tissues were 43% stronger, 21% more extensible, and 21% stiffer than tetrasporophytic distal tissues. However, the superior strength of gametophytic tissues was not evident at the stipe/holdfast junction (where breakage typically occurs), and the two phases were equally susceptible to dislodgment by a given force. The primary ecophysiological role of carrageenans in C. crispus may not be the provision of a structure to resist wave action.